p120 catenin affects cell-cell adhesion by interacting with the highly conserved juxtamembrane domain of classical cadherins, and has additional roles in both the cytoplasm and the nucleus. Three recent reports indicate that cytoplasmic p120 can modulate the activities of RhoA, Rac, and Cdc42, leading to altered cell morphology and increased motility. Cadherin binding blocks these cytoplasmic p120 effects, suggesting an elegant and previously unexpected mechanism for regulating the balance between adhesive and motile cellular phenotypes. These observations also provide a potential explanation for the metastatic phenotype shown by cancer cells that have lost E-cadherin expression. Our long-term goal is to understand, and prevent or develop treatments for, tumor metastasis. Specifically, in this project, we seek to (1) elucidate the mechanism(s) by which p120 affects different Rho GTPases, (2) test the hypothesis that cytoplasmic p120 can promote invasiveness in vitro and in vivo, and (3) clarify the role of kinesin in p120 function. In Aim 1 structure-function analysis and selective uncoupled mutants of p120 will be used, and specific protein-protein interactions tested, to determine whether p120 affects RhoA, Rac and Cdc42 via the same or distinct mechanisms. In Aim 2, we will test in vitro whether cadherin-unbound p120 promotes cell motility and induces invasiveness. Treatments that affect p120 localization or function in cultured cells will also be tested for their effects on invasiveness, after injection of the cells into nude mice. Finally, in Aim3 we will test the role of the p120-kinesin association in the activity of Rho GTPases, cadherin function, cytoskeletal dynamics and cell motility. By exploring the role of p120 catenin in the integration of cadherin and Rho signaling cascades, we expect to determine whether p120 acts as a cell contact-sensitive switch, mediating contact inhibition of motility, and cadherin-mediated suppression of invasiveness. We expect that elucidating p120's functional and physical interaction domains will allow the future generation of compounds that target particular p120 functions, as the basis of novel cancer treatments. We believe that because p120 is bound to cadherins in normal cells, selectively targeting the p120 functions that promote invasiveness in the cadherin-uncoupled state would be uniquely effective in cadherin-deficient malignant cells.